American citizens are under closer scrutiny than ever before, thanks to modern technology and an increased focus on security. We have witnessed these changes in our everyday lives, from how we go to the airport to how our children go to school. If ordinary citizens are looked at this closely, they tend to assume the screening process must be extraordinarily tough for men and women who actually work at defense-oriented job sites.

Recent incidents, including last week's mass shooting at the Navy Yard in Washington, D.C., suggest otherwise.

Aaron Alexis killed 12 people at the Navy Yard before he was shot and killed by police. Despite a wide variety of red flags in his background, Mr. Alexis had received and maintained enough security clearance to hold an all-access pass at a half-dozen military installations, including the Navy Yard.

This month it is Aaron Alexis. Earlier this year it was Edward Snowden, the IT contractor who exaggerated his education on his resume to get a job with the National Security Agency and then used his access to steal documents and disseminate them to the public through WikiLeaks. In both cases we are left shaking our heads and wondering: If people like Mr. Alexis and Mr. Snowden can pass background checks to work in government offices with high security, who exactly gets rejected?

We learn about these issues only after something has gone wrong, but the questions that arise have a local impact on the Peninsula as well. The public affairs office for Fort Eustis and Langley Air Force Base says the two military installations have more than 1,450 "authorized contractor positions." The NASA Langley Research Center uses about 1,700 contact workers. Newport News Shipbuilding declined to say how many contractors work at the shipyard on a regular basis.

Each of these workers has to pass at least some level of background check, the intensity of which is determined by the nature and location of the work he or she will be doing. These are the same sorts of background checks that produced "thumbs-up" reviews for Mr. Alexis and Mr. Snowden.

Mr. Alexis was granted low-level security access in 2008 while he was still a member of the Navy Reserves. He was discharged in 2011 after at least eight instances of misconduct including insubordination, unauthorized absences and a disorderly conduct arrest. He received an honorable discharge.

It is hard to imagine that this history in the Navy Reserves didn't send a torpedo through his application for security clearance to work at military installations. Shouldn't a history of insubordination and other conduct issues within the U.S. military call into question the qualifications of a man who subsequently wants to do contract work for the military? But a year ago he was hired by a Hewlett-Packard subcontractor, which confirmed his security clearance with the Department of Defense. He cleared another background check in June, run by a private contractor.

Mr. Alexis had at least two gun-related incidents on his record. Both were investigated by police, but he was not prosecuted for either. He also had a long history of being treated for mental health issues by the Veterans Administration, and in a recent incident he told police that the disembodied voices in his hotel room were using microwaves to send vibrations through his brain.

The federal Office of Personnel Management, which oversees most of the government's security background checks, now outsources a lot of that work to private security firms. Former employees at USIS, the firm that approved background checks on Mr. Snowden and Mr. Alexis, told The Washington Post that they are under pressure to handle an overwhelming caseload on impossible deadlines. USIS is now under federal investigation.

President Barack Obama has called for further investigation into the way security clearances are determined. The Senate Homeland Security and Governmental Affairs Committee has said it may hold hearings on the subject. It is tragic that it took Monday's shooting incident at the Navy Yard to get a serious, in-depth discussion of this critical topic.

Now that these questions have been raised, we need answers. After the fact, it is all too clear that Mr. Alexis' background made him unfit to work in any sort of secure workplace. But any investigation needs to do more than just rehash the questions of how he got cleared. It needs to focus on how to fix this critical process so people who pose such obvious risks don't keep dropping into the system's apparent chasms.